1. Field of the Invention
The present invention generally relates to a relay device. More specifically, the present invention relates to a relay device, for example, that is preferably applied to transmission of a MAC frame received from a network within the relay device.
2. Background Information
A conventional internal configuration of a relay device having a function of transmitting a MAC frame received from a network, is illustrated in FIG. 2. In the frame transmission device 10 illustrated in FIG. 2, a CPU (Central Processing Unit) 11 conducts the final control of each component. A network interface 13 receives a frame F1 from an external network NW1. The frame F1 then proceeds via a DMA (Direct Memory Access) transmission. During the DMA transmission, the network interface 13 transmits the frame F1 to the main memory 12 through the bus BA1 without the CPU 11. Consequently, even when the CPU 11 is conducting other processes, the frame F1 can be transmitted to the main memory 12 to realize a high-speed frame transmission.
After the frame F1 is transmitted to the main memory 12, the CPU 11 determines how to handle the frame F1 based on the information read from each field of the frame F1. For example, according to this decision, the contents of the frame the F1 are processed in the frame transmission device 10, sent by other network interfaces (not illustrated) to other external networks different from the network NW1, or instantly deleted.
A conventional frame relay device, for example, is shown in Japanese Patent Application 2003-099396, which is hereby incorporated by reference
However, when the frame F1 transmitted to the main memory 12 via the DMA transmission includes deleted frames as described above, it can be said that using the bus BA1 to transmit the frame F1 is a waste of consumption of internal resources and judging by the CPU 11 after the DMA transmission, and effectively leads to resource availability deterioration due to the waste of the operation resources.
For example, when a VLAN (Virtual LAN) is set, since frames sent from senders of the same VLAN group having the same values of VLAN-IDs (VLAN numbers) are necessary, those frames are processed inside, or relayed, while frames sent from the different group senders having the different VLAN-IDs are to be deleted. Since the location of the field including the VLAN-ID (VLAN Tag) is fixed according to IEEE 802.1 Q in the frames and the format of MAC frame is shown in FIGS. 3(A) and (B), the frame relay device can recognize the VLAN-ID by checking the contents of the frames.
While, in the case of a frame relay device that only processes the VLAN frame, the deletion of the frame can be also determined by recognizing no VLAN tags in the ordinary MAC frames illustrated in FIG. 4.
In the case of broadcasting, a deletion similar to the aforementioned one might occur. The frame broadcast (broadcast frames) is the frame addressed to all non-designated terminals, and is often used in LANs for exchanging information, for example, in a DHCP or ARP. The terminal receiving the frame (frame relay) determines whether the frame sends the necessary information to the terminal itself or not by information other than the sending MAC address. When the frame is not necessary to the terminal, the terminal deletes the frame.
However, if the network interface 13 is only mulch-functioned to reduce waste of the resources arising in the aforementioned deletion, the circuit configuration of the network interface 13 will be complicated and flexibility deterioration or development costs increase will occur because the circuitry must be changed in case the communication protocol used in the network (ex. NA1) is expanded.
This will come from the fact that most of functions of the network interface 13 usually need to be realized by hardware. The reason most of the functions of the network interface 13 are realized by hardware is as follows. Since the function of the network interface 13 belongs to the lower layer of the model referred to OSI, for example, the data-link layer, the processing on this layer will be bottlenecked to the upper layer unless the processing speed on this layer is much faster than the software processing speed of the CPU 11, and it will bring much deterioration of the throughput of the communication application.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved relay device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.